Grains or cereal crops are an abundant source of carbohydrates worldwide. Katherine Lee Bates, a Wellesley College English professor, immortalized America’s grain-producing capacity in her words to “America the Beautiful.” Professor Bates was inspired to pen her words after experiencing the grandeur of America’s West while visiting Colorado College.
Hardly a day goes by without reading or hearing something about “carbs” and diet. We will investigate carbohydrates as fuels in later chapters, but, before we do, let us examine what “carbs,” or carbohydrates, are and see some nonfuel functions for these ubiquitous biomolecules. Carbohydrates are carbon-based molecules that are rich in hydroxyl (C−OH) groups. Indeed, the empirical formula for many carbohydrates is (CH2O)n—literally, a carbon hydrate. Simple carbohydrates are called monosaccharides. Complex carbohydrates—polymers of covalently linked monosaccharides—are called polysaccharides. A polysaccharide can be as simple as two identical monosaccharides linked together. Or it can be quite complex, consisting of dozens of different monosaccharides that are linked to form a polysaccharide composed of millions of monosaccharides. Monosaccharides are the monomers that make up poly saccharides, just as amino acids are the monomers that make up proteins. However, the nature of the covalent bonds linking the monosaccharides in a polysaccharide are much more varied than the canonical peptide bond of proteins. The variety of monosaccharides and the multiplicity of linkages forming polysaccharides mean that carbohydrates provide cells with a vast array of three-dimensional structures that can be used for a variety of purposes as simple as energy storage or as complex as cell–cell recognition signals.